The present invention relates to tubular ceramic capacitors having metallized internal surfaces and having improved end terminations.
Coaxial capacitors have conventionally comprised a tube of ceramic material such as BaTiO.sub.3, SrTiO.sub.3 or the like. Inner and outer electrodes are formed on the tube so as to be electrically insulated from each other. End termination means are affixed to the ends of the tubular body to make electrical connection to the respective electrodes. Such capacitors and methods of making the same are taught in U.S. Pat. Nos. 4,109,292 and 4,197,570.
The volumetric efficiency of such capacitors can be increased by increasing the electrode surface area by means such as employing a more intricate cross-sectional configuration. For example, U.S. Pat. No. 3,274,468 teaches a cylindrical monolithic capacitor comprising a plurality of ceramic dielectric layers interleaved with conductive electrodes. The process of making such a capacitor is expensive since electrodes and additional dielectric layers must be applied in sequential steps. Also, all electrode layers except the last applied layer must be formed of noble metal in order to withstand the firing of subsequently applied dielectric layers.
Tubular capacitors are generally provided with cup-shaped electrode terminations that are applied over the ends thereof. Such capacitors exhibit low volumetric efficiency due to the loss of the end space under one of the cups thus restricting the useful part of the dielectric. Another problem is breakage of the fragile tube by pressing on the cups.